Which molecule has the largest dipole? 

  A ClF3

  B BF3

  C SF6

  D CF4

(Total 1 mark)

1

Which of these atoms has the highest electronegativity? 

  A Na

  B Mg

  C Cl

  D Ar

(Total 1 mark)

2

Ethanedioic acid is a weak acid.Ethanedioic acid acts, initially, as a monoprotic acid.

 

3

(a)     Use the concept of electronegativity to justify why the acid strengths of ethanedioic acidand ethanoic acid are different.

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(b)     A buffer solution is made by adding 6.00 × 10–2 mol of sodium hydroxide to a solution

containing 1.00 × 10–1 mol of ethanedioic acid (H2C2O4).Assume that the sodium hydroxide reacts as shown in the following equation and that inthis buffer solution, the ethanedioic acid behaves as a monoprotic acid.

H2C2O4(aq) + OH–(aq)  HC2O4–(aq) + H2O(l)

The dissociation constant Ka for ethanedioic acid is 5.89 × 10–2 mol dm–3.

Calculate a value for the pH of the buffer solution.Give your answer to the appropriate number of significant figures.

 

 

 

 

 

pH = ....................................(5)

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(c)     In a titration, the end point was reached when 25.0 cm3 of an acidified solution containing

ethanedioic acid reacted with 20.20 cm3 of 2.00 ×10–2 mol dm–3 potassium manganate(VII)solution.

Deduce an equation for the reaction that occurs and use it to calculate the originalconcentration of the ethanedioic acid solution.

 

 

Equation .........................................................................................................

Calculation

 

 

 

 

 

 

 

 

Original concentration = ............................... mol dm-3

(4)(Total 15 marks)

A hydrogen peroxide molecule can be represented by the structure shown.

(a) Suggest a value for the H−O−O bond angle.

........................................................................................................................(1)

4

(b)     Hydrogen peroxide dissolves in water.

(i)      State the strongest type of interaction that occurs between molecules of hydrogenperoxide and water.

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(ii)     Draw a diagram to show how one molecule of hydrogen peroxide interacts with onemolecule of water.Include all lone pairs and partial charges in your diagram.

 

 

 

 

 

 

 

 

 

 

 

 (3)

(c)     Explain, in terms of electronegativity, why the boiling point of H2S2 is lower than H2O2.

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(Total 7 marks)

(a)     Ammonia gas readily condenses to form a liquid when cooled.

(i)      Name the strongest attractive force between two ammonia molecules.

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(ii)     Draw a diagram to show how two ammonia molecules interact with each other in theliquid phase.Include all partial charges and all lone pairs of electrons in your diagram.

 

 

 

 (3)

(b)     Ammonia reacts with boron trichloride to form a molecule with the following structure.

 

State how the bond between ammonia and boron trichloride is formed.

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(c)     The following table shows the electronegativity values of some elements. 

    H Li B C O F

  Electronegativity 2.1 1.0 2.0 2.5 3.5 4.0

(i)      Give the meaning of the term electronegativity.

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(ii)     Suggest the formula of an ionic compound that is formed by the chemicalcombination of two different elements from the table.

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(iii)     Suggest the formula of the compound that has the least polar bond and is formed bychemical combination of two of the elements from the table.

...............................................................................................................(1)

(Total 9 marks)

The following table shows the electronegativity values of the elements from lithium to fluorine. 

    Li Be B C N O F

  Electronegativity 1.0 1.5 2.0 2.5 3.0 3.5 4.0

(a)    (i)      State the meaning of the term electronegativity.

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(ii)     Suggest why the electronegativity of the elements increases from lithium to fluorine.

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(b)     State the type of bonding in lithium fluoride.Explain why a lot of energy is needed to melt a sample of solid lithium fluoride.

Bonding .........................................................................................................

Explanation ....................................................................................................

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(Extra space) ................................................................................................

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(c)     Deduce why the bonding in nitrogen oxide is covalent rather than ionic.

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(Extra space) ................................................................................................

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(d)     Oxygen forms several different compounds with fluorine.

(i)      Suggest the type of crystal shown by OF2

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(ii)     Write an equation to show how OF2 reacts with steam to form oxygen and hydrogenfluoride.

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(iii)    One of these compounds of oxygen and fluorine has a relative molecular mass of70.0 and contains 54.3% by mass of fluorine.

Calculate the empirical formula and the molecular formula of this compound.Show your working.

Empirical formula .................................................................................

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Molecular formula .................................................................................

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(Total 14 marks)

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          The table below shows the electronegativity values of some elements. 

  H C N O

Electronegativity 2.1 2.5 3.0 3.5

(a)     State the meaning of the term electronegativity.

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7

(b)     State the strongest type of intermolecular force in the following compounds.

Methane (CH4) .............................................................................................

Ammonia (NH3) ............................................................................................(2)

(c)     Use the values in the table to explain how the strongest type of intermolecular force arisesbetween two molecules of ammonia.

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(d)     Phosphorus is in the same group of the Periodic Table as nitrogen.

A molecule of PH3 reacts with an H+ ion to form a PH4+ ion.

Name the type of bond formed when PH3 reacts with H+ and explain how this bond isformed.

Type of bond ...............................................................................................

Explanation ..................................................................................................

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(e)     Arsenic is in the same group as nitrogen. It forms the compound AsH3

Draw the shape of an AsH3 molecule, including any lone pairs of electrons. Name theshape made by its atoms.

Shape

 

 

 

 

Name of shape ............................................................................................(2)

(f)      The boiling point of AsH3 is –62.5 °C and the boiling point of NH3 is –33.0 °C.Suggest why the boiling point of AsH3 is lower than that of NH3

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(g)     Balance the following equation which shows how AsH3 can be made.

          ...... AsCl3   +   ...... NaBH4 → ...... AsH3   +   ...... NaCl   +   ...... BCl3(1)

(Total 14 marks)

 

 

          The table below shows the electronegativity values of some elements. 

  Fluorine Chlorine Bromine Iodine Carbon Hydrogen

Electronegativity 4.0 3.0 2.8 2.5 2.5 2.1

(a)     Define the term electronegativity.

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Page 9 of 26

(b)     The table below shows the boiling points of fluorine, fluoromethane (CH3F ) and hydrogenfluoride.

 

 

F–F H–F

Boiling point/K 85 194 293

(i)      Name the strongest type of intermolecular force present in:

Liquid F2 ..............................................................................................

Liquid CH3F ........................................................................................

Liquid HF ............................................................................................

(ii)     Explain how the strongest type of intermolecular force in liquid HF arises.

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(c)     The table below shows the boiling points of some other hydrogen halides. 

  HCl HBr HI

Boiling point / K 188 206 238

(i)      Explain the trend in the boiling points of the hydrogen halides from HCl to HI.

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(ii)     Give one reason why the boiling point of HF is higher than that of all the otherhydrogen halides.

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(Total 11 marks)

 

 

          (a)     Methanol has the structure

Explain why the O–H bond in a methanol molecule is polar.

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(b)     The boiling point of methanol is +65 °C; the boiling point of oxygen is –183 °C. Methanoland oxygen each have an Mr value of 32. Explain, in terms of the intermolecular forcespresent in each case, why the boiling point of methanol is much higher than that of oxygen.

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(Total 5 marks)

 

 

Page 11 of 26

          (a)     Both HF and HCl are molecules having a polar covalent bond. Their boiling points are293 K and 188 K respectively.

(i)      State which property of the atoms involved causes a bond to be polar.

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(ii)     Explain, in terms of the intermolecular forces present in each compound, why HF hasa higher boiling point than HCl.

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(b)     When aluminium chloride reacts with chloride ions, as shown by the equation below, aco-ordinate bond is formed.

AlCl3   +   Cl–   →   AlCl4–

Explain how this co-ordinate bond is formed.

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Page 12 of 26

(c)     Draw the shape of the PCl5 molecule and of the PCl4+ ion. State the value(s) of the bondangles.

PCl5                                                PCl4+

 

 

 

 

 

Bond angle(s) .................................    Bond angle(s) ..................................(4)

(Total 10 marks)

 

 

          (a)     An ammonium ion, made by the reaction between an ammonia molecule and a hydrogenion, can be represented as shown in the diagram below.

(i)      Name the type of bond represented in the diagram by N—H

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(ii)     Name the type of bond represented in the diagram by N→H

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(iii)     In terms of electrons, explain why an arrow is used to represent this N→H bond.

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Page 13 of 26

(iv)    In terms of electron pairs, explain why the bond angles in the NH4+ ion are all 109° 28’

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(b)     Define the term electronegativity.

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(c)     A bond between nitrogen and hydrogen can be represented as —

(i)      In this representation, what is the meaning of the symbol δ+ ?

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(ii)     From this bond representation, what can be deduced about the electronegativity ofhydrogen relative to that of nitrogen?

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(Total 11 marks)

 

 

Which one of the following bond polarities is not correct?

A          in ethane

B          in bromoethane

C          in ethanol

D          in ethanal(Total 1 mark)

12

Page 14 of 26

Mark schemes

A[1]1

C[1]2

Page 15 of 26

(a)     This question is marked using levels of response. Refer to the Mark Scheme Instructionsfor Examiners for guidance on how to mark this question.

All stages are covered and the explanation of each stage is generally correct andvirtually complete.

Answer is communicated coherently and shows a logical progression from stage 1and stage 2 to stage 3. Steps in stage 3 must be complete, ordered and include acomparison.

Level 35 – 6 marks

All stages are covered but the explanation of each stage may be incomplete or maycontain inaccuracies OR two stages are covered and the explanations are generallycorrect and virtually complete.

Answer is mainly coherent and shows a progression from stage 1 and stage 2 tostage 3.

Level 23 – 4 marks

Two stages are covered but the explanation of each stage may be incomplete or maycontain inaccuracies, OR only one stage is covered but the explanation is generallycorrect and virtually complete.

Answer includes some isolated statements, but these are not presented in a logicalorder or show confused reasoning.

Level 11 – 2 marks

Insufficient correct Chemistry to warrant a mark.Level 0

0 marks

Indicative Chemistry content

Stage 1: difference in structure of the two acids•        The acids are of the form RCOOH•        but in ethanoic acid R = CH 3

•        whilst in ethanedioic acid R = COOH

Stage 2: the inductive effect•        The unionised COOH group contains two very electronegative oxygen atoms•        therefore has a negative inductive (electron withdrawing)effect•        The CH 3 group has a positive inductive (electron pushing) effect

Stage 3: how the polarity of OH affects acid strength

• The O–H bond in the ethanedioic acid is more polarised / H becomes more δ+

•        More dissociation into H + ions•        Ethanedioic acid is stronger than ethanoic acid

6

3

(b)     Moles of NaOH = Moles of HOOCCOO– formed = 6.00 × 10–2

Extended response1

Page 16 of 26

Moles of HOOCCOOH remaining = 1.00 × 10–1 – 6.00 × 10–2

= 4.00 × 10–2

1

Ka = [H+][A–] / [HA]

[H+] = Ka × [HA] / [A–]1

[H+] = 5.89 × 10–2 × (4.00 × 10–2 / V) / (6.00 × 10–2 / V) = 3.927 × 10–2

1

pH = –log10(3.927 ×10–2) = 1.406 = 1.41

Answer must be given to this precision1

(c)     5H2C2O4 + 6H+ + 2MnO4–   2Mn2+ + 10CO2 + 8H2O

OR 5C2O42– + 16H+ + 2MnO4

–   2Mn2+ + 10CO2 + 8H2O1

Moles of KMnO4 = 20.2 × 2.00 × 10–2 / 1000 = 4.04 × 10–4

1

Moles of H2C2O4 = 5 / 2 × 4.04 × 10–4 = 1.01 × 10–3

1

Concentration = moles / volume (in dm3)

= 1.01 × 10–3 × 1000 / 25 = 4.04 × 10–2 (mol dm–3)

If 1:1 ratio or incorrect ratio used, M2 and M4 can be scored1

[15]

(a) 94−105.5°14

(b)     (i)       Hydrogen bond(ing) / H bonding / H bonds

Not just hydrogen1

Page 17 of 26

(ii)     

OR

 

1 mark for all lone pairs

1 mark for partial charges on the O and the H that are involved in Hbonding

1 mark for the H-bond, from Hδ+ on one molecule to lone pair on Oof other molecule

3

(c)     Electronegativity of S lower than O or electronegativity difference between H and S islower

Mark independently1

No hydrogen bonding between H2S2 molecules

Or only van der Waals / only dipole-dipole forces between H2S2 molecules

If breaking covalent bonds CE = 01

[7]

(a)     (i)      Hydrogen bonds / H bonds

Not just hydrogen.1

5

Page 18 of 26

(ii)     

M1 – lone pair on each N.

M2 – correct partial charges must be shown on the N and H of abond in each molecule.

M3 – for the H bond from lone pair on N to the Hδ+ on the other NH3

molecule.

If not ammonia molecules, CE = 0 / 3.3

(b)     Lone pair / both electrons / 2 electrons / electron pair on N(H3) is donated to B(Cl3)

Allow both electrons in the bond come from N(H3).1

(c)     (i)      The power of an atom or nucleus to withdraw or attract electrons or electrondensity or a pair of electrons (towards itself)

1

in a covalent bond1

(ii)     LiF OR Li2O OR LiH

Allow Li2O2, allow correct lithium carbide formula.1

(iii)    BH3 / H3B

Allow B2H6 / H6B2

Do not allow lower case letters.1

[9]

(a)     (i)      The power of an atom or nucleus to withdraw or attract electrons OR electron densityOR a pair of electrons (towards itself)

Ignore retain1

6

In a covalent bond1

(ii)     More protons / bigger nuclear charge1

Page 19 of 26

Same or similar shielding / electrons in the same shell or principal energy level /atoms get smaller

Not same sub–shellIgnore more electrons

1

(b)     Ionic

If not ionic then CE = 0 / 3If blank lose M1 and mark on

1

Strong or many or lots of (electrostatic) attractions (between ions)

If molecules / IMF / metallic / atoms lose M2 + M3, penaliseincorrect ions by 1 mark

1

Between + and − ions / between Li+ and F− ions / oppositely charged ions

Allow strong (ionic) bonds for max 1 out of M2 and M31

(c)     Small electronegativity difference / difference = 0.5

Must be comparative

Allow 2 non-metals1

(d)    (i)      (simple) molecular

Ignore simple covalent1

(ii)     OF2 + H2O   O2 + 2HF

Ignore state symbolsAllow multiplesAllow OF2written as F2O

1

(iii)    45.7% O1

( O         F )( 45.7    54.3 )( 16      19 )

If students get M2 upside down lose M2 + M3Check that students who get correct answer divide by 16 and19 (not 8 and 9). If dividing by 8 and 9 lose M2 and M3 but couldallocate M4 ie max 2

1

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(2.85    2.85)( 1        1 )

EF = OF or FO

Calculation of OF by other correct method = 3 marksPenalise Fl by 1 mark

1

MF (= 70.0 / 35) = O2F2 or F2O2

1[14]

          (a)     Ability/power of an atom/element/nucleus to withdraw electrondensity or electron cloud or a pair of electrons (towards itself);

Not withdraw an electronIf ref to ionic, metallic , imf etc then CE = 0

1

From a covalent bond or from a shared pair of electrons;

Not distortNot remove electrons

1

7

(b)     Van der Waals/ vdw/London/ temporary (induced) dipole/dispersion forces;

1

Hydrogen bonds/H bonds;

Not just hydrogen1

(c)     (Large) electronegativity difference between N + H/ differenceof 0.9/ N very electronegative;

Insufficient to say N= 3.1 and H = 2.11

Forms N δ– / H δ+ or dipole explained in words;Not N becomes (fully) negative or vice versa

1

Lone pair on N attracts/forms weak bonds with H (δ+);

QWCCan score M2 and 3 from a diagram

1

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(d)     Co-ordinate/dative;

If not correct then CE = 0. If covalent/blank mark on.1

          Both electrons/ lone pair (on P/PH3)

Not lone pair on hydrogen1

          Shares/donated from P(H3)/ to H(δ+);1

(e)     3 bonds and 1 lp attached to As;

Must label H and As atomsAccept distorted tetrahedral not bent tetrahedral

1

          Pyramidal/tetrahedral/ trigonal pyramidal;

Not bipyramidal/triangular1

(f)      (Only) weak Van der Waals forces between molecules /AsH3

has weaker IMF /ammonia has hydrogen bonding/ moreenergy needed to break IMF’s in ammonia/ Van der Waalsweaker than H bonds;

Accept has no H bonds.Ignore dp-dp in AsH3 provided ammonia has stronger IMF.If between atoms mentioned CE=0Break bonds CE = 0

1

(g)     4AsCl3 + 3NaBH4 → 4AsH3 + 3NaCl + 3BCl3;

Accept multiples1

[14]

 

 

          (a)     tendency / strength / ability / power of an atom / element / nucleusto attract / pull / withdraw electrons / e - density / bondingpair / shared pair

1

in a covalent bond1

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Page 22 of 26

(b)     (i)      F2       =       van der Waals’ / induced/temporary dipole-dipole /                   dispersion / London forces

1

CH3F           dipole-dipole

(not just ‘dipole’)1

HF     =       hydrogen bonding

(not just ‘H’ / ‘hydrogen’)1

(ii)     large difference in electronegativity between H and F / Fmost/very/much more electronegative / values ‘4’ & ‘2.1’ quoted

(not just ‘high er’)1

δ+H-Fδ- dipole created or dipole clearly implied

(accept arguments such as ‘uneven charge in bond’/’polar bond’ F slightly negative / H slightly positive)

1

attraction/bond formed between δ+H and lone pair on F(M2 / M3 may be scored from a diagram)

(CE if full charges shown - lose M2 and M3)1

(c)     (i)      van der Waals’ / induced/temporary dipole-dipole / dispersion /London forces / attractions

(ignore references to dipole-dipole)1

increase with the increasing Mr / size / mass / N 0 of e- / size

of e- cloud (in the hydrogen halides)

(if ionic, or if ‘covalent bonds broken’ = CE = 0)

(mark M1 and M2 separately)1

(ii)     hydrogen bonding stronger than van der Waals’ attraction/forces

(accept hydrogen bonding is very strong / strongest)

(accept arguments such as ‘HF has H-bonds, others only have vander Waals’)

(not just ‘HF has H-bonding’)1

[11]

 

 

Page 23 of 26

          (a)     Oxygen more/very/highly electronegative (than hydrogen)OR oxygen has stronger attraction for bonding electrons / bondingelectrons drawn towards oxygen;

1

causes higher e– density round oxygen atom / causes Hδ+

Oδ–;1

9

(b)     van der Waals’ forces between oxygen molecules;1

Hydrogen bonding between methanol molecules;1

H-B stronger than van der Waals’ OR stronger IMF in methanol;

(if dipole-dipole forces in O2 or methanol, allow comparison,hence max 2)

(if ionic/covalent etc. max 1)

(mention of bond break = CE = 0)1

[5]

 

 

          (a)     (i)      Electronegativity (difference) or suitable description (1)

Accept F and Cl are highly electronegativeNot both atoms are highly electronegative

(ii)     HF = hydrogen bonding (1)HCl = (permanent) dipole-dipole bonding or even van de Waals’ (1)Hydrogen bonding stronger / is the strongest IMF (1)

Accept a statement that HF must have the stronger IMF, even if noIMFs identified

The explanation must be based on intermolecularforces/attractions

Note: if the explanation is clearly intramolecular = CE4

10

(b)     Electron pair or lone pair donated (1)

Do not accept ‘donation of electrons’

          From chloride ion to Al or AlCl3 (1)

M1 can be earned by a general explanation of coordinate bonding,even if the electron pair is said to come from Al. The second mark,M2, is for this specific bond

Ignore missing charge2

Page 24 of 26

(c)    4

                

PCl5 shown as trigonal bipyramid    PCl4+ shown as tetrahedral[Look for:  ONE solid linear Cl-P-Cl bond]        NO solid linear Cl-P-Cl bonds]

Bond Angle(s) 90° and 120° (1)                       Bond angle(s) 109 or 109.5° (1)[10]

 

 

          (a)     (i)      Covalent (1)

(ii)     Co-ordinate (1) (or dative)

(iii)     Both / two / pair electrons come from nitrogen (1)

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(iv)    4 bonding / electron pairs (1)

         repel equally (1)

OR are identical

         as far apart as possible (1)

OR to position of minimum repulsion

         tetrahedron (1)7

(b)     Power (or ability) of an element / atom to attract electron pair/electrons/an electron/electron density (1)

          in a covalent bond (1)

Allow attract from, withdraw in, do not allow removefrom, withdraw from.

2

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(c)     (i)      Electron deficient (1)

Or small, slight, partial positive charge

(ii)     H < N (1)2

[11]

 

 

A[1]12

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